The present invention relates to a print media drive arrangement for driving a print media through a print zone located between first and second roller means of a hardcopy apparatus.
When applying ink to a print media such as paper, it is known that the media tends to expand as it absorbs the ink to produce an effect known as “cockle”. Unless otherwise constrained, the print media tends to lift away from the underlying printing platen and this causes the spacing between the printheads and the print media to vary, which causes a deterioration in print quality. In extreme cases, the print media may even come into contact with the printheads.
To reduce this problem it is known, see for example U.S. Pat. No. 4,759,649, to provide a so-called overdrive roller arrangement at the exit of the print zone, in which the print media is maintained flat in the print zone by being tensioned by the output rollers being driven slightly faster, or overdriven, compared to the input or feed rollers. Such an overdrive arrangement enables the print media advance movements through the print zone to be accurately controlled. Between successive print media advance movements, the printheads of the hardcopy apparatus apply swaths of ink to the print media.
However, for certain printing tasks, in particular those requiring so-called “bleed” printing, it is necessary for ink to be applied in the top and bottom edge regions, or margins, of a print media. In such cases a problem can arise in that, when printing occurs in such regions, the print media is engaged only by one of the rollers, viz. only the feeder roller in a top margin adjacent to the leading edge of the print media or only the overdrive roller in a bottom margin adjacent to the trailing edge of the print media. This can lead to print media advance movements of reduced size, which cause dark banding in the printing due to overlapping swaths, or to print media advance movements which are too large, thus producing banding in the form of gaps in the printing.